Abstract: In a digital telephone set connected to a digital data exchange through a transmission line, a plurality of handsets, which are mounted on a telephone body, are for converting input sounds into input analog speech signals and for converting output analog speech signals into output sounds. Connected to the handsets, a plurality of analog-to-digital converters converts the input analog speech signals into input digital speech signals. Connected to the handsets, a plurality of digital-to-analog converters converts output digital speech signals into the output analog speech signals. On the telephone body are mounted a set of dialling keys for producing a numerical signal. Connected to the dialling keys, a control device is for producing input control data in response to the numerical signal and is for producing an output control signal in response to output control data.

Abstract: A communications system having a common equipment unit and a plurality of telephone station sets coupled to the common equipment unit comprises a common equipment unit having at least one trunk interface for coupling at least one central office telephone line to the common equipment unit and an analog to digital converter for converting analog signals on the telephone line into digital form, and at least one station interface coupling the common equipment unit to at least one of the station sets by a single wire pair.

Abstract: A ringing signal detection circuit for a subscriber's apparatus which is connected to a telephone office line together with an attached telephone set. An incoming signal on the telephone line is converted to a pulse signal with a repetition frequency twice the incoming signal by a full-wave rectifier and a differentiating circuit. The pulse signal is applied to a retriggerable mono-stable multivibrator through a photo-coupler and an inverter. The time period of a metastable state of the multivibrator by one trigger pulse is selected to be longer than the break period in the dial pulse signal but longer than a half cycle of the ringing signal. Therefore, the multivibrator is maintained at the high level for a longer time period at a time when the incoming signal is the ringing signal than the time when the incoming signal is the dial pulse signal.

Abstract: Signal data is generated by interconnected non-inverting and inverting voltage followers and is transmitted on power-carrying conductors to a remote detection circuit comprising a differential amplifier which receives equal in-phase signal inputs of opposite polarity, thereby effecting cancellation of any externally-induced noise which might accompany the signal data.

Abstract: The disclosure is directed to a calling circuit which controls the connection of two different audio signal sources to a single audio signal transmission path for broadcasting the audio signals over a telephone set loudpseaker as well as controlling the energization of indicators in the telephone set and at the main control circuit. Only four conductors are used to connect the telephone set with the main control circuit, two of which are power supply conductors which may supply other circuits as well.

Abstract: A counting circuit is disclosed which generates an electrical representation corresponding to the number of pulses in a plurality of pulse trains, each pulse train containing at most ten pulses. The circuit does not start to count the number of pulses in individual pulse trains until a first pulse train with more than a preselected number of pulses is received. The circuit then counts each pulse in subsequently received pulse trains for a preselected number of pulse trains. The circuit is particularly useful in key telephone dial pulse signalling apparatus as a register circuit which is not responsive to false pulses generated by lifting the handset.

Abstract: The disclosure relates to a dial impulse relay circuit including a three-winding relay which repeats a pulse train generated by a first circuit onto a second circuit with substantially no pulse ratio distortion.

Abstract: The disclosure is for key telephone system line control circuitry which provides telephone station line status signals for central office ring, busy, idle and station hold conditions by means of a single control line.